For 32gb ddr3 k = 
maybe -k 2048, you need to test.
can you please tell what is the optimal value of n and K for 256GB RAM?
I don't know maybe you need to test with -n 0x400000000000000 and some values some values of K upto fill all the memory. The program tell you more of less how much mamoery is going to need, so test one value and press ctrl C if you that it doesn't fill your RAM